[tag tool] Large feature to support applying a new tag to the whole library

[davelab6]

ATM the tag tool is best for editing existing tags. Recently @m4rc1e added a simple form input to add a new tag string, which results in an empty tag set list.

But what we need as a workflow, is a (large) feature in the tool to show all 1,700+ families and allow rapid-fire tag data creation at that scale.

For some tags, we need to be library-complete, and so need a workflow for going over all 1,700+ families. My guess is that we could use hotkeys so that eg pressing tab (using HTML tabindex properties) moves us directly to the next row's input box, backspace or space makes that family have a zero value (and thus disappears and doesn't appear in the CSV output), and with a desktop keyboard number pad for a right handed person, the workflow can be super fast where they tap tab with a left hand finger, space with a left hand thumb, and numbers on the numberpad with the right hand.

But for other tags, we can use existing tags to exclude some existing tags - we can say confidently that "anything with previously existing tag X will have a new tag Y value of 0 and therefore can be excluded from this workflow".

Likewise we might want to say "anything with previously existing tag X will have a new tag Y value of X and therefore can be included for this workflow starting with that value and then I'll edit it from there".